The Transport and General Workers' Union says it has evidence of a "permissive arrangement" whereby demonstrators were allowed to park their vehicles on the property of oil companies before going outside to join the picket line.

The union is drawing up a dossier which it will send to the prime minister raising a number of complaints about the level of security at refineries and questioning why injunctions were not taken out against the protesters.

As a government task force met to discuss how to prevent a repeat of the blockades, the TGWU's General Secretary, Bill Morris, said an inquiry would be preferable to "knee-jerk" legislation which he feared would curb legitimate industrial action in the future.

'Intimidation'

Mr Morris told BBC Radio 4's World at One: "At one refinery in Fawley near Southampton there were cars and tractors parked overnight in a nearby car park and for the first time in living memory, people were able to gain access to that refinery without any real security checks,"

He also said the TGWU had heard "evidence of concerns about intimidation when companies were saying to drivers 'you needn't go out'".